1. Field of the Invention
This invention relates to an apparatus for tightening and loosening caps on containers, more particularly to an apparatus having two opposite rotary members that are adapted to contact frictionally and slidingly caps on containers.
2. Description of the Related Art
FIG. 1 illustrates a conventional apparatus 1 for tightening and loosening a cap 21 on a container 22, such as a bottle. The cap 21 threadedly engages the container 22. The conventional apparatus 1 includes a connecting rod 16, a cap-connecting member 11 that is sleeved on the connecting rod 16 and that is adapted to be connected to the cap 21, a positioning inner sleeve 12 sleeved on the cap-connecting member 11, a connecting outer sleeve 14 sleeved on the positioning inner sleeve 12, a magnet 17 disposed between and connected magnetically to the connecting outer sleeve 14 and the positioning inner sleeve 12, and a rotary socket 15 connected to the connecting outer sleeve 14. In operation, the positioning inner sleeve 12 and the cap-connecting member 11 are driven to rotate through the magnet 17 upon rotation of the rotary socket 15. When the cap 21 is tightened on the container 22, and when the friction force between the cap 21 and the container 22 overcomes the magnetic attraction force between the magnet 17 and the positioning inner sleeve 12, the cap 21 can no longer rotate relative to the container 22 by the rotation of the rotary socket 15.
The conventional apparatus 1 is disadvantageous in that several sizes of the cap-connecting member 11 are required to be manufactured for corresponding sizes of the caps 21 and that it is laborious to replace the cap-connecting member 11 for a desired size of the cap 21. In addition, since the friction force between the cap 21 and the container 22 varies with the materials used for forming the cap 21 and the container 22, and since the magnetic attraction force between the positioning inner sleeve 12 and the magnet 17 is fixed and cannot be adjusted, the cap 21 may not be driven to a desired position on the container 22 when the aforesaid friction force is relatively large and exceeds the aforesaid magnetic attraction force.